Light control for timing display

ABSTRACT

Disclosed is an electronic wristwatch having no moving parts and incorporating a light-responsive solid-state control circuit for the time display. An electro-optic digital display in the form of light-emitting diodes is switched off when the ambient light falls below a predetermined level. The display is also turned off when the light is too bright and it is provided with a manual override switch for actuating the display under dark conditions at the option of the wearer.

UnIted States Patent 1191 1111 3,747,323

Eckenrode July 24, 1973 54] LIGHT CONTROL FOR TIMING DISPLAY 3,505,804 4/1970 110mm 58/50 3,646,75l 3/1972 Purland et al. [75] Inventor g e Eckenmde, Mlnersvme, 3,485,033 12/1969 Langley 58/50 x Assigneer HMW Industries, Lancaster, Primary Examiner-Richard B. Wilkinson Assistant Examiner-Edith C. Simmons Jackmon [22] Filed: Aug. 3 1971 Attorney-Le Blane & Shur [21] Appl. No.: 168,611 T CT 57 ABS RA Related US. Application Data I l [62] Division of Sch No. 145 425 May 20 1971- Disclosed is an electronic wristwatch having no moving parts and incorporating a light-responsive solid-state 52 us. c|.- 58/50 R 250/215 x circuit the time electro'OPiC 51] Int. Cl. G04b 19/30 digital display in the light-emitting dimes is ['58] Field of Search 58/23 R 23 A 50 switched off when the ambient light falls below a prede- 25 215 350/l6'0 R termined level. The display is also turned off when the '1 light is too bright and it is provided with a manual over- 5 References Cited ride switch for actuating the display under dark condi- UNITED STATES PATENTS tions at the option of the wearer. 3,575,491 4/1971 Heilmeier 350/160 10 Claims, 5 Drawing Figures PATENIED 3.747. 323 sum 1 or 2 ubcdefgh colon obcdefgubcdefg obcdefgobcdefg INVENTOR 82 JAMES H; ECKENRODE FIG.'4

ATTORNEYS.

PAIEMEM 3.141. 323

sum 2 or 2 DISPLAY LOGIC INVENTOR JAMES H. ECKENRODE ATTORNEYS.

LIGHT CONTROL FOR TIMING DISPLAY This application is a voluntary division of copending application Ser. No. 145,425, filed May 20, 1971, in the name of James H. Eckenrode and entitled LIGHT CONTROL FOR TIMING DISPLAYS.

This invention relates to an ambient light-responsive control circuit for timing displays and more particularly for use with a solid-state timepiece in the form of an electric wristwatch which employs no moving parts. In order to conserve power, the control circuit turns off the display at times when the watch is not likely to be used' or when the display cannot be read.

In the present invention, a frequency standard in the form of a crystal oscillator acts through solid-state electronic circuit dividers and drivers to power in timed sequence the light-emitting diodes of an electro-optic display. Low power consumption and small size and weight are achieved through the use of complementary MOS circuits to produce what is in essence a miniaturized fixed program computer and in the preferred embodim ent the wristwatch is constructed so that substantiallyall the electrical circuitry is made using largescale integrated circuit techniques.

Battery-powered Wristwatches and other small portable timekeeping devices of various types are well known and are commercially available. The first commercially successful battery-powered wristwatch was of the type shown and described in assignees United States Reissue Patent No. RE 26,187, reissued Apr. 4, 1967, to John A. Van Horn et al. for ELECTRIC WATCH; Electric watches of this type employ a balance wheel and a hair-spring driven by the interaction of a current-carrying coil and a magnetic field produc'ed by small permanent magnets.

In recent years, considerable effort has been directed toward the development of a wristwatch which does not employ an electromechanical oscillator as the master time reference. For example, there is disclosed in assigne'e's US. Pat. No.'3,560,998, issued Feb 2, 1971, an electronic watch utilizing an oscillator and frequency converter with low power complementary MOS circuits. The oscillator/frequency converter combination of-thatpatent is described as suitable for driving conventional watch hands over a watch dial, or, alternativelyj for selectively actuating the display elements of an {optical display in response to the drive signal output of the converter. In as'signees US. Pat. No. 3,576,099, issued Apr. 27, 1971, there is disclosed an improved watch construction in which the optical display is described as a plurality of light-emitting diodes which are intermittently energized to assure a minimum power consumption and an increasingly long life forthe watch battery.

The present invention is directed to an improved watch construction of-the same general type as disclosed in the above-mentioned patents and one which utilizes no moving parts to perform the timekeeping function. The wristwatch comprises a frequency standard, preferably operating at a frequency of 32,768 Hz and formed as a crystal-controlled complementary MOS inverter used as an oscillator. Output signals from the frequency standard pass through a frequency converter, preferably in the form of a multi-stage binary frequency divider constructed of complementary MOS transistors. The signal is divided down in the frequency Mounted on the face of the watch are one or more photosensitive electrical elements which sense the amount of ambient light impinging upon the face of the watch. The photosensors may be either photoresistors or phototransistors or other well known photoelectric solid-state circuit elements. The photosensors are connected to the display actuator driving the light-emitting diode display so that the display is automatically switched off under certain conditions of ambient light. A single photosensor may be used to turn off the display when the ambient light falls below a certain predetermined level. However, two photosensors are preferred, one acting to turn off the display when the ambient light falls below a predetermined level and the other turning off the display when the ambient light becomes too bright. As a result, the display, which may or may not be intermittently energized, is automatically turned off during periods when the watch is not in use or cannot be read so as to conserve the energy of the relatively small battery which may be fitted into a c0nventional man s wristwatch case.

his therefore one object of the present invention to provide an improved light control circuit for timing displays.

Another object of the present invention is to provide an arrangement for automatically turning off an electro-optical display in accordance with ambient light conditions.

Another object of the present invention is to provide a timing display control circuit particularly for use with light-emitting diodes.

Another object of the present invention is to provide a control circuit for timing displays which turns off the display when the incident light on the display falls below a predetermined level.

Another object of the present invention is to provide a control circuit for a timing display which automatically turns off the display when the ambient light becomes too bright. v

Another object of the present invention is to provide an improved solid-state wristwatch having a timing display control circuit.

Another object of the present invention is to provide an electronic wristwatch having no moving parts and incorporating an ambient light-responsive solid-state switch for turning off the display when the light incident on the display becomes either too bright or too dark. 5

These and further objects and advantages of the invention will be more apparent upon reference to the following specificatiomclaims, and appended drawings, wherein:

FIG. 1 is a perspective view of a conventional sized man's wristwatch constructed in accordance with the present invention;

FIG. 2 is a simplified block diagram showing the principal components of the wristwatch of FIG. 1;

FIG. 3 shows a seven bar segment light-emitting diode array forming a part of the display of the wristwatch of FIGS. I and 2;

FIG. 4 is a circuit diagram showing the details of the electrical connections from the display actuator to the display diodes; and

FIG. 5 shows the light control circuit for the timing display.

Referring to the drawings, the novel watch of the present invention is generally indicated at in FIG. 1. The watch is constructed to fit into a watch case 12 of approximately the size of a conventional mans wrist watch. The case 12 is shown connected to a wristwatch strap or bracelet 14 and includes a display window 16 through which time is displayed in digital form as indicated at 20. Mounted on the case 12 is a pushbutton switch 18 by means of which the display 20 may be actuated when the wearer of the wristwatch 10 desires to ascertain the time, as more fully discussed below.

FIG. 2 is a simplified block diagram of the principal components of the watch 10 of FIG. 1. The watch comprises a time base or frequency standard 26, preferably chosen to produce an electrical output signal on lead 28 at a frequency of 32,768 Hz. This relatively high frequency is supplied to a frequency converter 30 in the form of a divider which divides down the frequency from the standard 26 so that the output from the converter 30 appearing on lead 32 is at a frequency of 1 Hz. This signal is applied to the display actuator 34, which in turn drives the display 20 of the watch by way of electrical lead 36. In the preferred embodiment, the display takes the form of a seven bar segment array of light-emitting diodes, preferably formed of gallium arsenide phosphide, which emit light when energized in the visible red region of the spectrum. FIG. 3 shows a single display station or numeral 38 consisting of seven light-emitting diodes 40, 42, 44, 46, 48, 50, and 52 of elongated shape and arranged so that by lighting the appropriate combination of bars any one of the numbers 0 to 9 may be displayed. The seven bar segment display of FIG. 3 is of the active type in that the lightemitting diodes act as a light source or radiator of visible light.

FIG. 4 is a simplified block diagram of the watch 10 I of the present invention showing the electrical connection to the watch display. Principal portions of the electrical circuitry, including the active components of the oscillator or frequency standard 26 of FIG. 2, all of the frequency converter 30, and substantially all of the display actuator 34 in FIG. 2, are contained in the integrated circuitblock 60 of FIG. 4. This block may be formed of one or several integrated circuit chips but in the preferred embodiment all the components within the block 60 are formed by large-scale integrated circuit techniques. In addition to the integrated circuit 60, the watch comprises a battery 62 which, by way of example only, may comprise a conventional 3 volt wristwatch battery. This battery energizes the display 20 whichis shown in FIG. 4 as consisting of a pair of hours stations comprising the digits station 64 and tens station 66, a pair of minutes stations comprising the digits station 68 and ten station 70, and a pair of seconds stations comprising the digits station 72 and the tens station 74. In addition, the display 20 includes a pair of colon dots 76, each formed by a single light-emitting diode. The components of the frequency standard or oscillator 26 external to the large-scale integrated circuit 60 are the oscillator crystal 78, the oscillator variable trimming capacitor 80, and an oscillator bias resistor 82. Large-scale integrated circuit 60 is connected to the various stations of the display as illustrated in FIG. 4 by the electrical leads 84.

In some previous constructions, displays as used in portable solid-state timing devices have been set for continuous operation such that the display are continuously energized from the power supply or battery. This means that they are continuously using current from the power source. As a result, for long periods of time, the display may be drawing power from the limited supply of the battery which serves no useful purpose when the display is not being read or when it cannot be read.

The present invention is directed to a novel circuit construction for Wristwatches and similar portable timing devices which extends the life of the power source by controlling a switch in response to ambient light levels which turns off the display for that period of time when there is only a low ambient light or no ambient light at all. Some examples of when the display is turned off include occasions when the watch is in a darkened room, such as a theater, in a bedroom at night when the owner is sleeping, and when the watch is on the owners wrist but covered by a jacket, coat, or shirt sleeves.

Some displays when incorporated in portable solidstate timing devices have in the past usually been off except when they are switched on by means of a display control switch. This is done to conserve power because of their relatively high current drain. In the present invention, the display is permitted to run continuously, i.e., is normally on, except when switched off by the control circuit here disclosed. In addition to turning off the display during periods of darkness, the light display control circuit preferably includes an arrangement to also turn off the display when ambient light is so bright as to cause washout. The control circuit includes a manual switch so that the display may be turned on and read at the option of the wearer when the display has been turned off by the automatic control. That is, a manual switch is provided to override the automatic turnoff portion of the circuit should the wearer decide for some reason to activate the display when it would be otherwise turned off.

FIG. 5 shows th light control circuit for the wristwatch of FIG. 1 incorporating a timing display of lightemitting diodes. The station 38 in FIG. 5 is representative of any one of the stations 64, 70, 68, 72, and 74 in FIG. 4. Display station 66 in FIG. 4 is formed by a pair of commonly connected bar segments which are either on or off to display a l in accordance with the hours the light-emitting diodes in FIG. 5 are connected to the display actuator which includes a display logic 'circuit 86 connected by leads 88, 90, 92, 94, 96, 98, and to respective NOR gates 102, 104, 106. 108, 110, 112, and 114. The outputs of the NOR gages are connected to the seven bar segments by the leads 84. Each of the NOR gates is provided with three inputs and in addition to the inputs connected to the display logic circuit 86, a second input of each of the gates is connected by a lead 116 to the junction of a first potentiometer or resistance divider 118 comprising a fixed resistor 120 and a variable photosensitive resistor 122. A third input ofeach of the NOR gates is similarly connected by a lead 124 to a second potentiometer orresistance divider 126 comprising fixed resistor 128 and photosensitive resistor 130. The two potentiometers are connected between the positive terminal 132 of the watch battery 62 and the grounded or negative side of the battery as indicated at 134 and 136 in FIG. 5.

In operation of the circuit, a signal is transmitted from the display logic 86 ,to the various NOR gates which control the seven segment active display for 'each digit. With positive logic employed and photoresistors as the light sensors, the NOR gates are on or off as follows.

a.'When the ambient light is low, the photoresistor resistance of resistor 122 is high and the junction 138 is at a more positive potential. At the same time, the resistance of photoresistor 130 is also high and junction 140 is negative and no signal is received by the display so that the display is off.

b. When ambient light is bright enough to cause washout, the resistance of resistor 130 is low and junction 140 is more positive. At the same time, the resistance of resistor 122 is low and junction 138 is close to ground potential so again'no signal is passed through the NOR gates.

c. When the ambient light is normal (not too light or too dark), the resistance of resistor 130 is high and resistor 122 is low so that junctions 138 and 140 are both close to ground and a signal passes through the gate and the display is on.

While the circuit of FIG. 5 has been described utilizing photoresistors 122 and 130, it is apparent that one or both of these may be replaced by phototransistors.

As can be seen from the above description, when the ambient light level is such as that occurring in darkness or semi-darkness, i.e., below a predetermined level, both photoresistors 122 and 130 are in the high resistance state. In this condition, the positive potential on lead 116 prevents signals from the logic display 86 actuating the display station 38. Conversely, when the ambient light is so high as to cause washout," both photoresistors 122 and 130 are energized to their low resistance state and in this condition the high potential on lead 124 prevents the display from being energized. However, when the ambient light is in a predetermined range between the maximum and minimum values just described, photoresistor 122 is in 'the low resistance state and photoresistor 130 is in the'high resistance state. In this case, both leads 116 and 124 are at a low potential so that signals from the display logic circuit 86 are transmitted to the display station 38 and the diodes are illuminated. The override switch 18 is connected across photoresistor 122 so that closure of this switchwhenthe ambient light is in the dark or semidark condition shorts the high resistance of photoresistor 122 and the display is illuminated at the option of the wearer as long as the pushbutton switch 18 remains depressed and closed.

lt isapparent from-the 'above'that the present invention provides an improved solid-state watch construction and particularly an improved light control system for turning the watch display off when the watch is not being read. The control circuit draws a minimum of power and may be actuated directly from the 3 volt power supply of a conventional electronic watch source. Important features of the present invention include the provision of a display in which the display is normally on at all times but is turned off to conserve power during those times when the display is not likely to be read. A single photoresistor may be utilized (or phototransistor) on-the face of the watch to turn off the display only when the light falls below a predetermined level. The circuit preferably incorporates an override switch so that the display may be read at the option of the wearer even when the ambient light is below the predetermined turn-off value. The display circuit pref erably incorporates a second photoresistor or phototransistor for turning off the display not only when ambient light is too low, but also when the ambient light is too high so as to cause washout" during which times the display is difficult to read anyway.

The display control system of the present invention may be combined with intermittent energization of the display both automatically or at the option of the wearer and further may be used in combination with automatic brightness control circuitry which varies the brightness of the display in accordance with ambient light conditions. However, the control circuit of the present invention is particularly adapted for use with a watch which is normally in the on condition and which is turned off only during periods of non-use by the automatic control circuitry of this invention. It acts to con serve battery power in that the display is not energized during long periods of non-use. It is understood that the switching control circuit disclosed turns off only the display and that the timekeeping components of the watch, including the frequency standard or frequency source 26 of FIG. 2, the frequency converter 30 and the display actuator, are constantly energized so that time is always being kept and is ready for display at any time.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being in dicated by the appended claims rather than by the fore going description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Whatis claimed and desired to be secured by United States Letters Patent is:

1. In a timepiece having an active electro-optical time display, a photosensor, switch means coupling said photosensor to said display whereby said display is switched off when the light incident on said photosensor falls below a predetermined level, and a second photosensor, said switch means including means for switching off said display when the light incident on said second photosensor rises above a predetermined level.

2. A timepiece of sufficiently small size and power consumption for use as a wristwatch comprising a source of constant frequency electrical signals, a frequency divider coupled to the output of said source for producing a low frequency timing signal, and active electro-optical time display, a display actuator coupling said frequency divider to said time display, said display actuator comprising a switch for switching off said dis play, and light responsive means coupled to said switch for actuating said switch when the light incident on said display falls below a predetermined level, said actuator comprising a display logic circuit, said switch comprising a plurality of logic gates coupling said logic circuit to said display.

3. Apparatus according to claim 2 wherein said display comprises a plurality of light-emitting diodes.

4. Apparatus according to claim 1 comprising a second photosensor, said switch means including means for switching off said display when the light incident on ual override switch coupled to said resistance divider for momentarily shorting out at least a portion of said resistance divider.

9. A timepiece according to claim 7 comprising a second resistance divider including a second photosensor, and means coupling an intermediate point on said second resistance divider to said NOR gates.

10. A timepiece according to claim 9 wherein said intermediate points on said first and second resistance dividers are at different potentials for equal amounts of light on said photosensors whereby said NOR gates are switched off by said resistance dividers at different light levels. 

1. In a timepiece having an active electro-optical time display, a photosensor, switch means coupling said photosensor to said display whereby said display is switched off when the light incident on said photosensor falls below a predetermined level, and a second photosensor, said switch means including means for switching off said display when the light incident on said second photosensor rises above a predetermined level.
 2. A timepiece of sufficiently small size and power consumption for use as a wristwatch comprising a source of constant frequency electrical signals, a frequency divider coupled to the output of said source for producing a low frequency timing signal, and active electro-optical time display, a display actuator coupling said frequency divider to said time display, said display actuator comprising a switch for switching off said display, and light responsive means coupled to said switch for actuating said switch when the light incident on said display falls below a predetermined level, said actuator comprising a display logic circuit, said switch comprising a plurality of logic gates coupling said logic circuit to said display.
 3. Apparatus according to claim 2 wherein said display comprises a plurality of light-emitting diodes.
 4. Apparatus according to claim 1 comprising a second photosensor, said switch means including means for switching off said display when the light incident on said second photosensor rises above a predetermined level.
 5. Apparatus according to claim 2 wherein said display actuator includes a manual override switch for turning on said display when said light is below said predetermined level.
 6. A timepiece according to claim 2 wherein said logic gates are NOR gates.
 7. A timepiece according to claim 6 wherein said light-responsive means comprises a resistance divider including a photosensor, and means coupling an intermediate point on said resistance divider to said NOR gates.
 8. A timepiece according to claim 7 including a manual override switch coupled to said resistance divider for momentarily shorting out at least a portion of said resistance divider.
 9. A timepiece according to claim 7 comprising a second resistance divider including a second photosensor, and means coupling an intermediate point on said second resistance divider to said NOR gates.
 10. A timepiece according to claim 9 wherein said intermediate points on said first and second resistance dividers are at different potentials for equal amounts of light on said photosensors whereby said NOR gates are switched off by said resistance dividers at different light levels. 